In a large sauté
pan, add the olive oil and heat on medium/high.Season the chicken with salt and
pepper.When oil starts to shimmer,
add the chicken and brown quickly on both sides.Remove from the pan and add the onions
and mushrooms.Salt
& pepper to taste and cook until soft.Return the chicken to the pan, add the
vinegar and garlic, poultry seasoning and salt & pepper to taste, stirring
to mix the spices.Reduce the heat
to a high simmer and cover, cooking for 20 minutes or until the balsamic
vinegar has evaporated and the onions are caramelized.